Curved surgical instruments and method of mapping a curved path for stereotactic surgery

ABSTRACT

The method of mapping a curved path for stereotactic surgery involves the selection of a helical-shaped path. The first step is to obtain an accurate image of the pertinent structures of the patient&#39;s internal areas. The image includes the lesion or target region and a potential opening site. Using the image, the non-target areas surrounding the lesion area are determined and evaluated for the medical acceptability of passing through them. A curved path which is substantially helical in shape is then selected within the image such that the curve avoids these non-target areas but intersects the target region and the opening site. The corresponding surgical instrument which will be used to follow the selected curved path has a rigid body having a shape which is substantially identical to the path.

FIELD OF INVENTION

[0001] This invention relates to the field of stereotactic surgery, andparticularly to curved instruments and method of mapping a curved pathfor stereotactic surgery for situations where a straight path isimpossible or would be more invasive or risky than a curved path.

BACKGROUND OF THE INVENTION

[0002] 1. Nomenclature and Definition of Terms

[0003] Currently, stereotaxis is generally associated with neurosurgery,and particularly with intracranial surgery. However, in the followingdescription, the terms “stereotaxis” or “stereotactic surgery” or“stereotactic surgical procedure” shall not be used in that limitedsense; rather it should be understood that the term shall be used moregenerally to distinguish it from the “conventional” surgical procedureswhere a large incision is made in a patient. Hence, the terms“stereotaxis”, “stereotactic surgery”, “stereotactic surgical procedure”shall encompass those clinical procedures where a rigid instrument isinserted into a small opening and is navigated, by control of the partthat remains outside, to a pre-determined area of a patient's body.However, frequent references will be made to intracranial surgery as away of illustrating the invention and its mode of operation, andtherefore, such references should not be construed as a limitation onthe present invention.

[0004] 2. Description of the Related Art

[0005] Stereotactic surgery (also known as “stereotaxis”) is well knownto those skilled in the art. It is a special surgical procedure fortreating an interior portion of a patient, usually the brain and otherintracranial structures, by inserting a rigid probe into a smallopening. In conventional open surgery, the surgeon makes an incisionlarge enough for the surgeon to see the path leading to the area ofpathology. Stereotaxis, on the other hand, does not require the surgeonto actually see the entire path, so a small opening, only big enough toinsert the probe, is required. Hence, stereotactic surgical proceduresoffer the advantage of minimizing the damage to the tissues surroundingthe lesion area, and promotes faster recovery of the patient.

[0006] Because a surgeon performing stereotactic surgery does notdirectly view the inner portions of the brain, he must be able to mapout a path and note the sensitivity of the tissues surrounding thedamaged area. He must also be able to navigate the probe such that theposition of the probe corresponds exactly with the designated path. Toachieve the necessary control, a number of apparatus and methods haverecently been developed. CAT scan technology, magnetic resonance imaging(MRI), angiography, digital subtraction angiography (DSA) and similardiagnostic procedures are currently used to obtain the visual image ofthe intracranial area. Such devices are coupled to apparatus, typicallya rigid helmet-like framework worn on the skull, or (less invasively butless precisely) markers attached to the skin and ‘frameless’ guidancesystem or robot, which precisely positions the probe in accordance withthe visual images.

[0007] Currently, only straight probes are used in stereotaxis. Hence,only a straight path leading to the selected point can be used. Whenchoosing a straight path, the surgeon selects a path which best avoidssensitive areas or other obstructions. If the path meets a bone, anopening can often be formed by drilling a hole. But if the selected pathmeets blood vessels, nerves, or brain tissues with important brainfunctions, a different path must be chosen, or risk causing irreparabledamage to the brain.

[0008] Not all areas can be reached via a straight path, however. Somesites are so well surrounded by important tissues that no straight pathexists where the risk is low. In other situations, a straight path mayexist, but the damaged area may be buried deep within the brainrequiring a penetration through thick layers of tissues. In still othersituations, the path may be confronted by a hard tissue such ascalcified dura mater which the probe is unable to penetrate. Lesions insuch unreachable places may either be classified as inoperable or betreated using the traditional open procedure.

[0009] In some of these situations, a curved path may better avoid theobstructions or sensitive tissues, and reach the intended area withlower risk to the patient. However, at the present, only straightdevices are in use, which can follow only a straight path, unless theyare allowed to move sideways and create a sheet of damage. To make onlya line of damage, the body of the device must slide along the pathpierced by the tip. For most curved instruments, however, such slidingmovement along a designated curved path is difficult or impossible.

[0010] Hence, in light of these shortcomings, it would be desirable tohave curved surgical instruments and a method of mapping a correspondingcurved path which will not cause significant damage to the surroundingtissue, and which will allow a stereotactic procedure to become a viableoption in a greater number of cases.

SUMMARY OF THE INVENTION

[0011] The method of mapping a curved path for stereotactic surgeryinvolves the selection of a helical-shaped path. The first step is toobtain an accurate image of the pertinent structures of the patient'sinternal areas. The image includes the target region and a potentialopening site. Using the image, the non-target or high-risk areassurrounding the target region are determined and evaluated for themedical acceptability of passing through them. A curved path which issubstantially helical in shape is then selected within the image suchthat the curve avoids these regions. The corresponding surgicalinstrument which will be used to follow the selected curved path has arigid body having a shape which is substantially identical to the path.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 shows the region of the brain accessible by a straightprobe through a single hole in the skull.

[0013]FIG. 2 shows the region of the brain accessible by curved probesthrough a single hole in the skull.

[0014]FIG. 3 is an image of the brain having a lesion located deepinside the brain, and curved access to it.

[0015]FIG. 4 is an image of the brain having a lesion near the cerebralcortex, in a region where cortex penetration is dangerous.

[0016]FIG. 5 is an image of the brain having a lesion closely beneaththe folded cortex, where a curved probe meets less tissue than astraight one.

[0017]FIG. 6 is an image of the placement of drug or radiation sourcesat multiple sites in a lesion, which would require two straightpenetrations but only one curved one.

[0018]FIG. 7 is an image of the brain requiring biopsy at multiplesites, which would require two entry points for straight access but onlyone for curved access.

[0019]FIG. 8 shows biopsy access in more than one direction to the samelesion through a single hole, by curved paths.

[0020]FIG. 9 shows the geometrical form of a helix.

[0021]FIG. 10A shows a restraining block, in two parts, through which arigid helical instrument can pass only by sliding along the helixdefining the hole in the block.

[0022]FIG. 10B shows the restraining block of FIG. 10A where the twoparts are mated into one piece.

[0023]FIG. 11 shows a pair of restraining blocks through which a rigidhelical instrument can pass only by sliding along the helix defining theholes in the blocks.

[0024]FIG. 12 shows a helical instrument being robot-guided along ahelical path.

[0025]FIG. 13 shows a helical instrument being hand-guided throughflexible tissue, where the user is assumed to have a continuouslyupdated image of its position.

[0026]FIG. 14 is a mathematical diagram illustrating the formation of ahelix using a virtual reality apparatus.

[0027]FIG. 15 is a mathematical diagram illustrating the determinationof a helix by two end points, an intermediate point and the degree oftwist.

[0028]FIG. 16 is a mathematical diagram illustrating the determinationof a helix by an end point, the direction of meeting it, another point,and the degree of twist.

[0029]FIG. 17 is a mathematical diagram illustrating the determinationof a helix by two end ends and an intermediate point.

[0030]FIG. 18 is a mathematical diagram illustrating the determinationof a helix by the settings of a mathematically modeled stereotacticframe.

[0031]FIG. 19 shows a rigid helical monopolar electrode.

[0032]FIG. 19A is a cross-sectional view of the electrode in FIG. 19.

[0033]FIG. 20 shows a rigid helical bipolar electrode.

[0034]FIG. 21A is a perspective view of a helical biopsy samplinginstrument.

[0035]FIG. 21B is a perspective view of an inner shaft disposed insidethe helical biopsy sampling instrument of FIG. 21A.

[0036]FIG. 22 is a perspective view of a helical needle for extractionor insertion of fluid.

[0037]FIG. 23A is a perspective view of a helical surgical instrumentwith a resection loop in its active position.

[0038]FIG. 23B is a perspective view of a helical surgical instrumentwith a resection loop in its retracted position.

[0039]FIG. 24 is a perspective view of a helical temporary implantplacement instrument.

[0040]FIG. 25 is a perspective view of a helical permanent implantplacement instrument.

[0041]FIG. 26 is a perspective view of a helical instrument fordelivering cold.

[0042]FIG. 27 is a perspective view of a helical instrument having adrilling tip.

[0043]FIG. 28 is a perspective view of a helical instrument used solelyfor piercing.

[0044]FIG. 29 is a perspective view of a helical instrument having aguide wire.

[0045]FIG. 30 is a perspective view of a helical instrument having aguide wire in addition to a core serving another instrumental function.

[0046]FIG. 31 is a perspective view of a helical surgical instrumentwith a cutting tool, gripping, spreading or clipping tip.

[0047]FIG. 31A is a perspective view of a nibbling tool for the helicalinstrument illustrated in FIG. 31.

[0048]FIG. 31B is a perspective view of a gripping tool for the helicalinstrument illustrated in FIG. 31.

[0049]FIG. 31C is a perspective view of a spreading tool for the helicalinstrument illustrated in FIG. 31.

[0050]FIG. 32 is a perspective view of a helical surgical instrumentwith a laser tip.

[0051]FIG. 33 is a perspective view of a helical endoscopic instrument.

[0052]FIG. 34 is a perspective view of a helically mounted light source.

[0053]FIG. 35 shows the combination of a light delivery channel with ahelical tube serving another function.

[0054]FIG. 36 is a perspective view of a helical instrument fordelivering pulverizing.

[0055]FIG. 37 is a perspective view of a helical instrument fordelivering low intensity ultrasound for imaging purposes.

DETAILED DESCRIPTION OF THE INVENTION

[0056] The present invention relates to a method of mapping a curvedpath for stereotactic surgery so a rigid curved instrument, having thesame shape as the path, can be navigated to the intended area. Theutilization of a curved path for stereotaxis offers a number of optionsand benefits unavailable for a straight instrument. Generally, the fieldof access is greatly increased for a curved path. FIG. 1 illustrates thefield of coverage for a straight instrument 5 (the region marked A)which is inserted into the cranium 6 through a small opening 7. FIG. 2illustrates the field of coverage for a curved instrument 10 (the regionmarked B) which is inserted into the same cranium 6 through the sameopening 7. As demonstrated by these two figures, the curved instrumentcan be made to cover a greater area than a straight instrument. Hence,the availability of a curved path allows stereotactic procedure tobecome a viable option in greater number of situations.

[0057] There are a number of situations where a curved path will be thepreferred option because any straight path to the area to be accessedpasses through a considerable amount of brain tissue. One such situationis illustrated in FIG. 3, where a lesion is located deep within thebrain, in the pineal body 15. Here, along any straight path such as L,an instrument penetrates sensitive structures such as the cerebellum 16or blood vessel 17, and risks serious damage. The curved path H entersthe cranium 18 to the left of the mid-sagittal plane S and utilizes aless risky channel, via cerebrospinal fluid 19, to the lesion area.

[0058] In other instances, a straight path may exist, but it would bemore invasive than a curved path. A common situation exemplifying thisprinciple is illustrated in FIG. 4. Here a tumor 20 lies fairly closelybelow the cerebral cortex 23 of the brain 25. A direct straight pathwould risk unacceptable damage to the sensory cortex 21 or motor cortex22, and the consequential loss of sensation or control in thecorresponding parts of the body. The current solution is to approach thetumor 20 via the path L, that is through the frontal lobe 26. This pathpasses through a great deal of white matter 27, with risk to thelong-range connectivity of the brain that is hard to assess for theindividual patient since the connection geometry is variable. If acurved path can be used, however, it can access the tumor via the pathH, through the frontal lobe 26. This path meets far less brain tissue,and the frontal lobe 26 is currently the path of choice (for straightinstruments) when accessing other target points. Similarly, in FIG. 5 alesion 30 lies closely under the cortex 31 but cannot be reached by astraight path that passes quickly through the cortex 31; the curved pathH can reach it more directly.

[0059] In still other situations, a straight path may simply be morelabor-intensive. In FIG. 6, several drug or radiation sources, 36, 37,38 can be placed by a single procedure along a curved path H, in adirection which would require a straight one to pass through the visualcortex 35. In FIG. 7, the two target sites 41 and 42, where scan datasuggest a need for biopsy samples, are individually reachable but noacceptable straight path meets both. They thus require two openings inthe cranium 43, and two separate brain penetrations, 44, 45, alongstraight paths L1 and L2. In contrast, the curved path H allowscollection of material from both sites from a single opening, withoutmeeting the motor cortex 46, the sensory cortex 47, or the visual cortex48. This avoids the additional cost, risk, and effort of using two pathsrather than one.

[0060] In FIG. 2, multiple penetrations are necessary even with a curvedprobe, but they can both use the same drill hole in the skull and passthrough essentially the same place in the cortex, even though they go towidely divergent points. FIG. 2 shows the increased volume of the brainreachable through a single skull hole.

[0061]FIG. 8 shows that with curved probes H1 and H2, a single opening51 in the cranium 52 can suffice for biopsy of a suspect region 53 inmultiple directions, mapping its extent in each.

[0062] In view of the figures above, the benefits of the curved path aremultitudinous. But it should be understood that not every set of curvedpaths will be a viable option. In order for any curved path to beconsidered, the path must meet an important criterion. It is imperativethat a rigid curved instrument having a shape identical to the shape ofthe path can be navigated through the brain matter without significantlydeviating from the determined course. Specifically, the instrument mustbe able to travel along the path without cutting across the surroundingtissues. To make only a line of damage, the body of the rigid surgicalinstrument must slide along the path pierced by the tip. For most curvedshapes, such rigid instrument sliding along a path is impossible; if agolf club form, for instance, slides along the line of its shaft, thehead leaves a sheet of damaged points. If the head slides in its owndirection, the shaft creates sideways damage. Hence, the curve must besuch that the rigid instrument slides only along the path traced by itstip.

[0063] To achieve this goal, the shape of the surgical instrument, andhence, the shape of the path must be that of a helix. As illustrated inFIG. 9, helix H is a well-known shape which is defined as a curve woundevenly around an arbitrarily placed cylinder of constant radius r,making a constant angle α with the cylinder's axis. A helix has thecharacteristic in that as the angle α approaches 0 degrees, the helixapproaches the limiting shape of a straight line. In the other extreme,as the angle α approaches 90 degrees, the helix approaches the limitingshape of a circular arc. Therefore, a straight line and a circular arcare a special case of the general form of a helix.

[0064] These two features, of motion with damage only at the tip, and ofcontrollability by a fixed passive constraint, are consequences of thesame ‘slide along itself’ property of the class of helical curves(including the degenerate straight and circular cases). They are bothimportant where the precision of brain surgery is required, but in lesscomplex tissues (where hand insertion guided by continuously updatedimages may be preferable to a pre-planned path), only the first isneeded. In FIG. 13 the helical instrument 80 pushed by hand 85 is beingguided through muscle 81 and avoiding blood vessels 82 for a target 83,guided by an ultrasound imaging system 84; it is not critical which partof the muscle tissue it meets, and muscle is sufficiently flexible thatif the hand turns the instrument slightly, in a motion that is notmerely a slide along the helix, the tissue can follow this sidewaysmotion without tearing. The surgeon can then continue the slidingpenetration, arriving more accurately at the target as a result ofresponse to image feedback.

[0065] Although it is preferred that the shape of the path and theinstrument be that of a near-perfect helix, some deviation is possiblewithout substantial degradation of the useful properties of the helicalshape. Some examples will be described for the purpose of illustratingthis principle.

[0066] As described above, a perfect helix is a curve wound evenlyaround an arbitrarily placed cylinder of constant radius r, making aconstant angle α with the cylinders axis. However, the shape may haveslightly deviating r and/or angle α without substantially affecting theoutcome, so long as the deviation is not excessive. The exact range ofdeviation which can exist without unduly affecting the effectiveness ofthe curved instrument, however, will vary depending on several factorssuch as the rigidity of the surgical instrument, the type of procedurebeing conducted, and the flexibility of the tissues being penetrated.

[0067] Further, it may be possible to deviate from a perfect helix to agreater extent where the deviation is periodic. An example would be anear-helical shape where the radius r and the angle α deviate by a fixedamount at an evenly-spaced interval, where at every other interval, theradius r and the angle α deviate oppositely to the one before.

[0068] In addition, it may be possible, and perhaps useful, to have acurved instrument only a portion of which has a helical shape. Otherslight modifications, not specifically mentioned herein, may also bepossible, so long as the general helical shape is intact.

[0069] In mapping the proper curved path having the helical shape, thefirst step is to generate an accurate medical image of the portion ofthe affected area of a human body. The image should cover all of thepertinent regions, and particularly the region to be accessed by thesurgical instrument, the surrounding region, and potential entry sites.

[0070] A multitude of methods currently exists for obtaining medicalimages. Some common examples are scans using MRI, PET, CAT, plainradiographs, etc. Other means may include commercially prepared bodymaps or detailed 3-D models. Whichever the method, it must providedetailed information as to the respective location, shape, and size ofthe varying tissues, organs, blood vessels, and other important matters,such that a surgeon can determine the path which avoids the undesiredregions.

[0071] Although the images obtained may be viewed in their originalformat, it is preferred that they be viewed in digitized form, andinterfaced with other devices such as a computer or digital signalprocessor. In this way, they may be easily manipulated and superimposedwith other images or otherwise manipulated for easy viewing.

[0072] After an accurate image is obtained, the region to be accessed,or target area, and some potential opening sites must be identified. Thesurrounding region is then observed and analyzed for sensitive tissues,organs, blood vessels, and other matters which need to be avoided by thesurgical instrument. A helical curve is then superimposed onto the imagesuch that the curve is able to access the desired region via one of thechosen opening sites without intersecting any of the sensitive areas. Inchoosing the path, it is useful to try a number of helices havingdifferent combinations of radius r and the angle α until a helix meetingall of the criteria is determined.

[0073] When selecting the path, it may be possible to have severalhelical curves which meet the criteria. In such a case, several factorsmay be considered in choosing the particular helical path which will beused for the surgical procedure. One important factor is the overalldistance of the path through the tissue. Generally, the shorter thebetter. Another factor which may be considered is the pitch, or theacuteness of the angle α. It is generally preferred that the helix withthe least acute angle α be chosen. A number of other factors may also beconsidered, such as the risks associated for a particular path takinginto consideration the type and nature of the tissue in the regions thepath will intersect.

[0074] To choose the optimal path, quantitative values may be assignedto these and other relevant factors. For each path using a particularhelix, a total utility value may be assigned to each of thecombinations. After a number of combinations is considered, the utilityvalues may be compared, and the path-helix combination having thehighest utility value may be chosen.

[0075] While the general method of mapping described above is useful,the medical potential of helical surgical instruments would besignificantly diminished without a practical way to choose an accesspath appropriate to a patient's particular needs and his or herstructural geometry, both of which vary. Successful choice requires away to specify a particular path, a way to assess what tissues it meets,a way to see what change may improve an unsatisfactory choice, and a wayto make such a change; all of which must be easy to use, to minimizeerrors and the time spent by the surgeon. The choice must then betranslated easily and clearly into specific procedure in the operatingroom.

[0076] The 3-dimensional relation of path and data preferably requires a3-D graphic display, which for ease of depth-perceptual judgment shouldbe stereographic. Given a particular target point P, there are fivedegrees of freedom in selecting a helix ending at P, or six if a startis also chosen. This suggests control by the six degrees offreedom—three translational, three rotational—of an object held inspace. Many control interfaces could be suggested by one skilled in theart; the essential is that the user should be able to move freely in theset of helices.

[0077] Within the display, since many important brain structures are notdirectly visible in a patient's scan data, there must be a labeled setof constructs aligned with the data as a guide to the patient's anatomy.No one such electronic brain atlas is an essential, but some electronicbrain atlas should be included, together with software features evidentto one skilled in the art, such as the highlighting and labeling ofstructures met by the current helix, and facilities to modify which onesare displayed and their transparency.

[0078] While there exists a number of ways to implement theabove-described system, it is preferred that a virtual realityapparatus, such as the one described in the following publication beadopted: T. Poston and L. Serra, The Virtual Workbench: Dextrous VR,proceedings Association for Computing Machinery, Virtual RealitySoftware and Technology (ACM VRST) 1994, G. Singh, S. K. Feiner, D.Thalmann eds., World Scientific, 1994, pp. 111-122. This is an apparatusby which the user grasps a 6-degree-of-freedom sensor behind a mirrorwhich reflects a stereographic display. A handle appears in the displayprecisely where the user's neuromuscular spatial sense reports that thesensor is currently held, and in the same orientation, so that thehandle can be manipulated with hand-eye coordination, which is importantfor dextrous, intuitive control. In the display, the handle is equippedwith a virtual tip whose shape depends on the tool function to which itis currently assigned. Either one or two sensors can be supported; inthis case, it is useful to have such a handle in each hand. Generalfunctions like file management, selection and rotation of objects, etc.,are provided by the software.

[0079] A number of approaches to selection of a path are possible, inwhich the use of six-degree-of-freedom user input is required to varyingdegrees. For the ‘hand-held’ method described below, it is essential;for the others it is helpful, but could be replaced by a more cumbersome2-D mouse input. Since the range of physically available instrumentgeometries will always be finite, in most cases it will be necessary tofind the available helix geometry nearest to that of the ‘ideal’ helixH, and adjust its position near H to satisfy the avoidance criteria.

[0080]FIG. 14 illustrates one process for selecting a helical path usingthis apparatus. In the display, the user sees a virtual selection tool65 whose displacement and movement correspond precisely with that of asensor handle (not shown) which the user manipulates. The virtualselection tool has a tip which is used mark points of reference. Theuser first brings the virtual selection tool tip T to a target point Pof interest within the display volume, and clicks a button on the sensorhandle to mark the point. After the point P has been marked, the usercan move the virtual selection tool to create a helical path having anycombination of radius r and the angle α.

[0081] As shown in FIG. 14, the helix H is created around an imaginarycylinder having a unique set of parameters depending on the position ofthe tool tip T, and the direction in which the tool points. At any givenposition of tip T, a line L is formed (and preferably displayed) in thepointing direction, and L becomes the axis of the cylinder around whichthe helix H is to be wrapped. The radius R of the cylinder joins P tothe nearest point N on L, and is continually redefined as the user movesthe handle and thus redefines L. A tip radius line S (equal in length toR), is orthogonal to L; we define Q as the point where it meets thecylinder. Line S is initially parallel to R, but since it is rigidlyattached to the virtual selection tool at the tip T, the point Q movesaround the cylinder as the selection tool is twisted about its axis L.For each successive position of the tool (until the selection button isreleased, fixing the choice), a helix H is created and displayed whichjoins Q to P around the cylinder, with an amount of turn equal to thetotal angle that Q has traveled around L in the moving coordinate frameof the selection tool.

[0082] If v is the vector from T to Q, and w the vector from T to N, letu be the vector $\frac{v \times w}{w}$

[0083] orthogonal to both, and l be the length of L. H may beparametrised as the curve,

H(t)=N+cos(t)v+sin(t)u+(t/l)w

[0084] or coordinates as,

=(N ₁+cos(t)v ₁+sin(t)u ₁+(t/l)w ₁,

(N ₂+cos(t)v ₂+sin(t)u ₂+(t/l)w ₂,

(N ₃+cos(t)v ₃+sin(t)u ₃+(t/l)w ₃),

[0085] from t=0 (giving the point P) to t=l (giving the point Q), whichmay be displayed in the normal way for three-dimensional curves; computeH(t) for a closely-spaced sequence of t values from 0 to l, and callstandard 3-D drawing routines (for instance, from the library OpenGLinstalled on many graphics machines) to project these points on thescreen for a left or right view (both, when viewing is stereo), maskedby ‘Z-buffer’ routines when the curve passes behind another graphicalobject.

[0086] Some other selection procedures, useful in particularcircumstances, are listed below. It may sometimes be convenient for thesurgeon to make an initial specification by one procedure, such as theone just described, and then make fine adjustments using another, suchas one of the following.

[0087] When it is important to choose a particular entry point E on theskull or outer boundary of the brain, selecting E and the target P, FIG.15, leaves three degrees of freedom in the choice of a helix. Fixing anintermediate point M determines two of these degrees of freedom; sincethere is a unique flat circular arc A through E, M and the target P, theremaining parameter essentially measures the out-of-plane twisting α ofthe helix chosen. The helix H can thus be selected by using theselection tool to choose M, and then adjusting α either by twisting thetool handle about its own axis, or by adjusting a slider. As well asbeing ‘entry and intermediate’ points, E and M could be chosen asco-targets with P for the action of the instrument.

[0088] Alternatively, one may wish to fix the entry point E, the targetpoint P, and the tangential direction by which H approaches it, FIG. 16.This direction, easily controlled by moving the tip D of a line drawnfrom P, leaves one degree of freedom uncontrolled; by stipulating thatthe cylinder radius equal the length of the line PD, the system gives acorrespondence between user movements of D and the set of helicesjoining P to E.

[0089] Another such correspondence, FIG. 17, is created by using anintermediate point M, as in FIG. 15, but letting the total twist equalthe logarithm of the ratio between the distances, A & B of M from E andP. This avoids the need for a separate twist control.

[0090] Given a choice of target P and values for radius and pitch, and aposition for the ring frame on which the arc A sketched in FIG. 18 ismounted, each possible position of the point G at which the guide block,discussed below, is rigidly attached to the frame corresponds to aunique choice of position for the helix H, for some angle of the arcwith the axis L and angle on the arc at which the guide block is placed.Thus a frame model with widgets at G that can control radius and pitch,and G itself draggable from one point in space to another, provides acontrol scheme closely corresponding to actual mechanical settings, andthus particularly intuitive for frame users. It has the advantage thatthe widgets at G can be set to provide only radius and pitch values thatare available in probe hardware at the site where the intervention is tobe performed, avoiding the need for separate selection of the ‘idealhelix’ and then the best physically available approximation to it.

[0091] Techniques well known to those skilled in the art can detectwhich geometrical structures imported from a brain atlas as polyhedraare intersected by H, and highlight them to bring the fact to the user'snotice. Inspecting the patient's scan data along the curve can beaccomplished by a texture-based ‘slicing tool’ for the virtual realityapparatus environment.

[0092] In some instances, a number of the helices found by the chosenscheme for interaction may meet the minimum criteria. After a particularhelix H has been selected, a detailed study should be conducted todetermine the desirability of the particular helical path chosen, takinginto consideration the various factors described above. Particularly,the helical path preferably should at least avoid most, if not all, ofthe sensitive surrounding areas, and intersect one of the intendedopening sites.

[0093] The methods of mapping a curved path as described above may beapplied in a wide range of stereotactic procedures, and generally thesame or similar methods can be adopted regardless to the type ofprocedure being performed. However, each of the procedures may involve adifferent rigid surgical instrument. But regardless to the type andnature of the instrument, it must have the helical shape having the samepitch and radius as the helical path to utilize the useful properties ofthe helix.

[0094] Furthermore, to drive a helical instrument along the path chosen,it must be rigidly held or constrained by a controller. A human or roboteffector may move with it (as in FIGS. 12 and 13), holding it and movingwith it; or its motion may be constrained by passing through a single ora plurality of guide blocks as illustrated in FIG. 10 and FIG. 11,respectively. FIG. 10A shows a block exploded into the two parts 70 and71 in which it is most easily manufactured, with a helical instrument 72between them. Two pieces of rigid metal, non-ferromagnetic if they areto be used in the presence of MR imaging devices, may be milled by aflat bed milling machine to the shapes shown; taking their common centeras origin, suppose the helix has the parametrized form

(x(s), y(s), z(s))=(r cos(s+p), r sin (s+p), as)

[0095] where p defines the phase angle by which the helix is related tothe x-axis where it passes through the (x,y) plane, and that theinstrument has thickness 2h. Then from the material for part 70 oneremoves the material within h of any point (x(s), y(s), z(s)), creatinga channel 73 through which the instrument will pass as shown by thecurved arrow, and also the material with$x > {r\quad {\cos \left( {\frac{z}{a} + p} \right)}}$

[0096] to create the surface 74 along which part 70 will meet 71.Similarly, in creating 71 one must remove the material within h of anypoint on the helix, creating part 75 of the hole through which theinstrument will pass, and also the material with$x < {r\quad {\cos \left( {\frac{z}{a} + p} \right)}}$

[0097] to create the surface 76 along which 71 will meet 70. Thesurfaces must be smoothly polished, for a close fit of the two parts andfor smooth passage with minimal play for the helical instrument passingbetween them. Although the outer portions of the two parts are shown asrectangular, forming a combined rectangular guide block 77 in FIG. 10B,any other outer shape which may conveniently be clamped into a rigidlyspecified position may equally be used.

[0098]FIG. 11 shows a pair of such blocks with their phases p adjustedso that a helical instrument of the same radius, pitch and thicknesswill pass through both of them when they are clamped in line at anappropriate distance d; if the clamps can rotate about the helix axis byan angle A, this distance changes by the amount${A\left( \frac{a}{2\pi} \right)}.$

[0099] Such rotation would make it convenient for each block to besymmetrical about the axis of the helix it contains, but this is nototherwise necessary; where the radius r is large, and the helix not farfrom straightness, the block can be more practically sized if it theaxis does not pass through it.

[0100] As the instrument is inserted first into a guide block, FIG. 10,or set of blocks FIG. 11, rigidly held by a robot or stereotactic frame,and then passes into a specimen, the guide block or set of blocksrestricts the portion passing through it to a segment of a helical path(as a straight guide hole controls the direction of a straight needle),pushing the instrument compels its tip to move along the continuation ofthe same helical curve. Hence, as with a straight instrument, a surgeoncan maneuver the instrument along a pre-determined path, with damageonly along that path. Pushing the instrument produces pressure at itstip, rather than along its sides. A high degree of agreement betweenplanned and actual motion is thus possible. The same motion may beachieved by active constraint (FIG. 12), where a carefully planned‘wrist motion’ of a robot effector 60 drives the instrument along itsplanned helical path 62 to reach a target 63 blocked for straightinstruments by the spine 64. However, with present technology thepassive constraint is the preferred implementation since (a) it is lesscostly to achieve a given degree of precision in such a constraint thanin a robot with a six-degree-of-freedom effector, and (b) the surgeonpushing the instrument through the passive constraint can feel thetissue's degree of resistance to penetration, which can be a valuablesensory cue to what tissue the instrument is meeting, and hence whetherinsertion should continue.

[0101] The following is a sample of some of the stereotactic procedureswhich may utilize the mapping method described, and their correspondinginstruments.

[0102]FIG. 19 shows a monopolar electrode 150, which may be used formeasurement or to deliver small currents for stimulation or largercurrents that flow through the tissue to a remote ground, applying heaton the way until the current is too spread to be significant: this isuseful for such purposes as killing a tumor by heat, but the volumeheated is too large and imprecisely defined for brain surgery. (Itremains useful for work in, for example, muscle.) As illustrated in FIG.19 and FIG. 19A, the instrument has an insulating rigid body 151surrounding a conducting core 152, and a conducting tip 154.

[0103] An important risk in stereotactic brain surgery is that of damageto a blood vessel. In open surgery the surgeon can detect such damagevisually, and repair it by various methods; when an instrument is beingdriven through tissue, both detection and repair are more difficult. Twofeatures will thus sometimes be desirable in a helical instrumentintended for penetration of the brain: (a) detection of bleeding (bytaking fluid samples, and examining them in situ or extracted via atube), (b) cauterization using heat from bipolar electrical current.FIG. 20 shows a helical instrument 160 for facilitating a bipolarscheme, with a power cable 161 surrounding a fluid channel 162 supplyingelectrodes 164 of alternating polarity (marked + and −). The currentthen flows only very near the electrodes, which is useful for sharplylocalized work, and in particular for cauterizing a wound made by theinstrument itself. The instrument has an opening for fluid samples 163,and electrodes 164 of alternating polarity around a non-conducting ring165.

[0104]FIG. 21A illustrates a helical biopsy sampling instrument 170. Ithas a rigid curved tube 171 of a helical shape and a rotatable windowhead 172. As illustrated in FIG. 21B, the instrument 170 has a flexible,turnable, and withdrawable inner shaft 173 with a collection chamber forstoring the sample. Rotating 173 within 172 opens and closes the chamber174 relative to the position selected for the helix before insertion.

[0105]FIG. 22 illustrates a helical needle which can be used to extractmaterial for analysis (biopsy) or because it requires removal, or todeliver medicine or other fluids, to areas of the body where a straightneedle would have difficulty in reaching. It has a hollow core 183inside a rigid body 181, and a sharp point and an opening at the tip182.

[0106]FIG. 23A and FIG. 23B illustrate a resection instrument 185 havinga rigid curved tube 186 with a flexible, turnable inner shaft 189. Inthe active position, FIG. 23A, the resection wire forms a loop 187 atthe tip 188 of the instrument 185; in its retracted position, FIG. 23B,the loop 187 is closed and displaced inside the rigid tube 186.

[0107]FIG. 24 illustrates a temporary implant placement instrument 190which can release radiation or drugs through the tip 191 of theinstrument, from the material chamber 192.

[0108]FIG. 25 illustrates a permanent implant placement having a rigidouter tube 196, a rigid or flexible inner core 197 and a detachable drugsource or device 198 at the tip, which can be pushed off by advancingthe core 197.

[0109]FIG. 26 illustrates an instrument 200 for cooling or heating anisolated area of a body. The instrument includes a cable or heat pipecore surrounded by an insulating sheath 201. At the tip is athermocouple or pipe tip 202 for chilling.

[0110]FIG. 27 illustrates a drilling instrument 205 with a rotatingflexible shaft 206 inside the rigid body 207 and a cutting burr 208attached at its end.

[0111] Another use for a rigid helical penetrating instrument is inconjunctions with non-rigid ones; a class that includes catheters andendoscopes. A non-rigid instrument is guided by its surroundings, movingwithin fluid (most often blood or cerebrospinal fluid (CSF)) between thewalls of the fluid space (most often a blood vessel or a ventricle). Itcan rarely be guided to push through parenchymal tissue in a plannedway, even if it has a sharp tip, because flexibility allows it to turnaside at a wall or a variation in tissue resistance. This limits thepoints it can reach, and the routes by which it may arrive there. Arigid device, however, can be pushed through tissue, and even drillthrough bone (for instance, using an instrument illustrated in FIG. 27).This opens a channel which can then be exploited by a flexible device.This is currently a standard procedure with straight rigid instruments:a straight channel is pierced by a probe, reaching a cavity such as aventricle and entering it in a convenient direction; it is thenwithdrawn, and a flexible instrument pushed in through the channel thathas been opened. This flexible instrument can then follow the cavity bythe usual mechanics of such instruments, reaching a target withoutfurther tissue damage.

[0112] The use of a helical instrument increases the options in suchchannel creation. This may be done by simply piercing the tissue with ahelical instrument as illustrated in FIG. 28, that is a simplepenetrating device; but in some cases the flexible instrument may notfollow the resulting channel accurately, since it must flex to do so. Inthis case it is appropriate to pierce with a hollow helical instrumentshown in FIG. 29 down which a flexible guide wire 210 can be inserted.When the channel has been created, the surgeon can remove the helicalinstrument while leaving the guide wire 210 in place, and then slide aflexible instrument along it. (A channel to contain a guide wire is acommon feature of the design of such flexible instruments, but the‘Seldinger technique’ of using a guide wire to change the instrumentthat follows a given path has not been extended to paths created byrigid instruments, which have been only straight.). A guide wire channel217 may also be included in a rigid helical instrument 215, illustratedin FIG. 30, containing a channel 219 serving the passage of energy,electrical current, or biological/therapeutic material, in eitherdirection.

[0113] A helically opened channel may be useful in endoscopic work, evenwhere there is already an access to some cavity for flexibleinstruments, since it is often necessary to have several instrumentssimultaneously in place: light, camera, and active tools guided by whatis seen in the camera view. Both to avoid overcrowding the access path,and to gain a more felicitous set of relative positions of thesedevices, there is use for delivering some of them by helical pathscreated by rigid insertion, rather than by insertion of a flexiblecatheter. The extra degrees of freedom provided by a helix over astraight path will allow the surgeon more freedom in the setting up ofpositions, with less damage in arriving there. The helical implementsuseful in such work will include: scissors, by which tissue can be cut;nibblers, by which bone or tissue can be cut away; forceps, by whichtissue can be grasped; and spreaders, by which tissue can be forcedapart.

[0114]FIG. 31 illustrates an instrument 220 having a rigid, helical tube221, a fixed hand grip 222, a turning hand grip 223, and a cutting tool224. A wire 225 is attached to the hand grip 223 and to the cutting tool224. The cutting tool 224 can be made to open and close by rotating thehand grip 223 around its pivot 226 as demonstrated by the two explodedviews. Various other tools may be attached to the instrument 220 inplace of the cutting tool 224, such as the nibbling tool 227 in FIG.31A; a gripping tool 228 in FIG. 31B; and the spreading tool 229 in FIG.31C.

[0115]FIG. 32 illustrates a helical instrument with a steerable lasertip 230 which is fed by a cable 234 in a rigid helical body 235. Thelaser delivers highly localized radiation 231 with which to burn awayunwanted material, separate tissues, or cauterize wounds.

[0116]FIG. 33 illustrates an endoscope with a camera 240 at its tip andan electrical or optical fiber connection 241 disposed inside a rigidbody 242. An endoscope requires light to see by, preferably lighting theview from the side. FIG. 34 shows a light casting tip 245.

[0117]FIG. 35 illustrates the incorporation of an optic fiber or powerchannel 250 for a light source 251 shedding light on the action of animplement such as the gripper shown in FIG. 31B (placed on both sides ofthe gripper jaw), reducing the number of separate instruments that mustenter the brain. Such a lighting feature may be added to any of theinstruments here described.

[0118]FIG. 36 illustrates an ultrasonic aspirator, with a vibratingsource 255 of directed ultrasound 256 to pulverize tissue, a liquidinsertion tube 257 to make a slurry of it, an extraction tube 258 bywhich to suck out the result, and fluid channels 259 with the powerchannel 260 inside the rigid helical tube 261.

[0119]FIG. 37 illustrates a source 271 of lower intensity ultrasound272, so that ultrasound receivers elsewhere can collect data from whicha detailed image of the region around the source can be reconstructed.

[0120] It should be understood by those skilled in the art that theabove list of applications is presented here only as a way ofillustrating the wide range of ways that the present invention can beused, and therefore, should not be construed as being a complete list ofthe possible application. Hence, various modifications, additions andsubstitutions are possible for the invention described herein, withoutdeparting from the scope and spirit of the invention as disclosed in theaccompanying claims.

We claim:
 1. A method of mapping a curved path for stereotactic surgery using a substantially rigid surgical instrument to access an area of a patient's body comprising: a) obtaining an accurate image of an area of the body, said image including an opening site and a target region; b) determining high-risk areas around said target region; c) selecting a non-linear curve within said image, wherein said curve is substantially helical in shape; whereby said curve intersects said target region and said opening site, but not said high-risk areas, said curve defining the curved path for which a rigid stereotactic surgical instrument having an identical shape to said curve will be navigated to said target region.
 2. The method as recited in claim 1 wherein the non-linear curve in said selection step is a helix.
 3. The method as recited in claim 1 wherein said image obtaining step is performed using an imaging technique selected from the group consisting of: MRI, PET, CAT, plain radiography, SPECT, MEG, EEG, US, fMRI, angiography, colour doppler, and reference maps of the body.
 4. The method as recited in claim 3 further comprising the steps of digitizing said image and interfacing said digitized image with a computer.
 5. The method as recited in claim 1 wherein said determining step and selecting step are performed simultaneously.
 6. The method as recited in claim 5 wherein a virtual reality apparatus is used to execute at least one of the steps.
 7. The method as recited in claim 2 wherein said selecting step includes: a) marking a target point P in said target region; b) selecting straight line L as a helix axis; and c) tracing a curve around said line L maintaining a constant radius r and angle α with respect to said line L, said curve intersecting said target point P.
 8. The method as recited in claim 7 wherein said selecting step b) and said tracing step c) are performed substantially simultaneously.
 9. A method of mapping a curved path for stereotactic surgery using a substantially rigid instrument, said method being aided by a virtual reality apparatus, said apparatus including a a display means, and a stylus adapted for allowing a user to interact with said virtual reality apparatus via said display means, said virtual reality apparatus adapted for displaying medical images on said display means and superimposing a helical curve of a selected radius r and angle α within said images, said method comprising: a) displaying an accurate image of an affected area of a patient's body on said display means, said image including a target region; b) determining high-risk areas around said target region; c) pointing said stylus to a point P in said target region; d) moving said stylus until a helical curve originating from point P is displayed on said displaying means such that no part of the helical curve intersects said high-risk areas, said curve defining the curved path for which a rigid stereotactic surgical instrument having an identical shape as said curve will be navigated to said target region.
 10. The method as recited in claim 8 further comprising: a) determining a location for an opening site; b) determining whether said helical curve intersects the opening site; and c) moving said stylus and selecting another helical curve until no part of the helical curve intersects said high-risk areas but intersects said opening site.
 11. A method of mapping a least-invasive curved path for stereotactic surgery using a substantially rigid instrument comprising: obtaining an accurate image of an affected area of a patient's body, said image including a target region and an opening site; determining high-risk areas around said target region; assigning a medical acceptability value to each of said high-risk areas; selecting a plurality of curves within said image wherein each of said curves is substantially helical in shape, and said curves intersecting said target region and said opening site; assigning a medical acceptability value to each of said curves based on its interaction with said high-risk areas; comparing said curves based on said medical acceptability value; and choosing a curve with an optimal value, said curve defining the curved path for which a rigid stereotactic surgical instrument having an identical shape as said curve will be navigated to said target region.
 12. The method as recited in claim 11 wherein each of said curves is helical in shape.
 13. A method of mapping a curved path for intracranial stereotactic surgery using a substantially rigid surgical instrument comprising: obtaining an accurate image of an affected area of a patient's intracranial area, said image including a target region and an opening site; determining high-risk areas around said target region; selecting a curve within said image wherein said curve is substantially helical in shape, whereby said curve intersects said target region and said opening site, but not said high-risk areas, said curve defining the curved path for which a rigid stereotactic surgical instrument having an identical shape as said curve will be navigated to said target region.
 14. The method of mapping a curved path for intracranial stereotactic surgery as recited in claim 13 wherein said curve is helical in shape.
 15. A non-linear surgical instrument for stereotactic surgery conducted along a curved path comprising: a substantially rigid, elongated body, said body being substantially helical in shape, wherein said instrument is adapted for being inserted into a small opening on a patient's body and navigated precisely along a selected curved path having substantially same shape as said instrument to perform a surgical function.
 16. The surgical instrument as recited in claim 15 wherein said rigid body is helical in shape.
 17. The surgical instrument as recited in claim 15 further comprising a monopolar electrode disposed at an end of said rigid body; a conductor core electrically coupled to said electrode and disposed inside said rigid body; wherein said rigid body is made of electrically insulating material; whereby said instrument is adapted for measuring or delivering electrical signals.
 18. The surgical instrument as recited in claim 15 further comprising a plurality of electrodes of alternating polarity disposed at an end of said rigid body, said electrodes adapted for delivering electrical current to a localized area; a protruding opening for collecting fluid samples disposed at said end; a fluid channel disposed inside said rigid body leading to said opening; and a power cable electrically coupled to said electrodes, said cable disposed inside said rigid body and around said fluid channel.
 19. The surgical instrument as recited in claim 15 wherein said instrument is a biopsy sampling instrument further comprising a flexible, withdrawable, and turnable shaft disposed inside said rigid body; a collection chamber at an end of said shaft, said chamber adapted for receiving and storing a sample fluid; and a rotatable window head at an end of said rigid body and over said collection chamber.
 20. The surgical instrument as recited in claim 15 wherein said instrument is a needle adapted for extracting material or delivering medicine or other fluids, further comprising a hollow core disposed along inside said rigid body; a sharp point at a tip of said rigid body; and a opening at said tip.
 21. The surgical instrument as recited in claim 15 wherein said instrument is a resection instrument further comprising a flexible, turnable shaft disposed along inside said rigid body; a resection wire having a loop, said loop being cable of being in an active and retracted positions, said loop being outside said shaft in the active position, and inside said shaft in the retracted position.
 22. The surgical instrument as recited in claim 15 wherein said instrument is a temporary implant placement instrument further comprising a tip at an end of said rigid body, said tip having a material chamber adapted for releasing radiation or drugs through said tip.
 23. The surgical instrument as recited in claim 15 wherein said instrument is a permanent implant placement instrument further comprising a core slidably disposed inside said rigid body; a detachable drug source or device disposed at an end of said rigid body, such that said drug source or device is detached by advancing said core.
 24. The surgical instrument as recited in claim 15 wherein said instrument is a cooling or heating instrument for cooling or heating an isolated area of the patient's body further comprising a tip disposed at an end of said rigid body; a core inside said rigid body for delivering heat or cold; and an insulating sheath surrounding said cable.
 25. The surgical instrument as recited in claim 15 wherein said instrument is a drilling instrument further comprising a rotatable flexible shaft inside said rigid body; and a rotatable cutting burr attached to an end of said shaft.
 26. The surgical instrument as recited in claim 15 further comprising a hollow core disposed inside said rigid body adapted for guiding a flexible guide wire, said rigid body capable of being removed from the patient's body while leaving said guide wire in the curved path.
 27. The surgical instrument as recited in claim 26 further comprising a channel inside said rigid body, said channel adapted for delivering electrical current or biological material in either direction.
 28. The surgical instrument as recited in claim 15 further comprising a fixed hand grip disposed at an end of said rigid body; a turning hand grip pivotally disposed adjacent to said fixed hand grip; a tool disposed at an end opposite to said fixed and turning hand grip; and a wire attached of said turning hand grip and said tool, such that said tool can be opened or closed by rotating said turning hand grip around a pivot.
 29. The surgical instrument as recited in claim 28 wherein said tool is a pair of scissors.
 30. The surgical instrument as recited in claim 28 wherein said tool is a nibbler.
 31. The surgical instrument as recited in claim 28 wherein said tool is a gripping apparatus.
 32. The surgical instrument as recited in claim 28 wherein said tool is a spreading apparatus.
 33. The surgical instrument as recited in claim 15 further comprising a laser tip disposed at an end of said rigid body, said laser tip adapted for delivering localized radiation for burning away unwanted material, separating tissues, and cauterizing wounds.
 34. The surgical instrument as recited in claim 15 wherein said instrument is a endoscope further comprising a camera at an end of said rigid body; a optical fiber connection for transmitting and receiving optical information disposed inside said rigid body and coupled to said camera; and a means for lighting disposed at said end.
 35. The surgical instrument as recited in claim 15 wherein said instrument is an ultrasonic aspirator further comprising a vibrating source at an end of said rigid body adapted for delivering directed ultrasound for pulverizing tissues; a liquid insertion tube disposed at said end for making a slurry of said tissues; an extraction tube for extracting the slurry of tissues; a fluid channel disposed inside said rigid body for delivering said slurry of tissues; and a means for delivering power for said aspirator.
 36. The surgical instrument as recited in claim 15 further comprising a vibrating source at an end of said rigid body adapted for delivering low level ultrasound for creating detailed image; a means for delivering power for said vibrating source.
 37. A guide block for a surgical instrument for stereotactic surgery, said instrument being substantially helical in shape, comprising a rigid body, a channel disposed in said rigid body, said channel having an identical shape as said surgical instrument, said channel adapted for fittingly receiving said surgical instrument and allowing said instrument to smoothly slide through said channel without deforming out of shape.
 38. The guide block as recited in claim 37 wherein said rigid body is made of two parts which are mated together.
 39. The guide block as recited in claim 38 wherein said parts are mated by being solidly mounted on a common rigid support. 